It's a sink or swim moment for the filmmakers behind the sequel to "Piranha 3D." Combining a silly, self-aware sensibility with over-the-top gore, the original comedic horror film starring the likes of Richard Dreyfuss, Christopher Lloyd and Elizabeth Shue as townsfolk fighting off prehistoric flesh-eating fish became a just-add-water cult hit when it was released two summers ago opposite more mature fare such as "The Expendables" and "Eat Pray Love."